1. Field of the Invention
The invention relates generally to blowout preventers used in the oil and gas industry. Specifically, the invention relates to a blowout preventer with a novel bonnet securing mechanism.
2. Background Art
Well control is an important aspect of oil and gas exploration. When drilling a well in, for example, oil and gas exploration applications, devices must be put in place to prevent injury to personnel and equipment associated with the drilling activities. One such well control device is known as a blowout preventer (BOP).
Blowout preventers are generally used to seal a wellbore. For example, drilling wells in oil or gas exploration involves penetrating a variety of subsurface geologic structures, or xe2x80x9clayers.xe2x80x9d Each layer generally comprises a specific geologic composition such as, for example, shale, sandstone, limestone, etc. Each layer may contain trapped fluids or gas at different formation pressures, and the formation pressures increase with increasing depth. The pressure in the wellbore is generally adjusted to at least balance the formation pressure by, for example, increasing a density of drilling mud in the wellbore or increasing pump pressure at the surface of the well.
There are occasions during drilling operations when a wellbore may penetrate a layer having a formation pressure substantially higher that the pressure maintained in the wellbore. When this occurs, the well is said to have xe2x80x9ctaken a kick.xe2x80x9d The pressure increase associated with the kick is generally produced by an influx of formation fluids (which may be a liquid, a gas, or a combination thereof) into the wellbore. The relatively high pressure kick tends to propagate from a point of entry in the wellbore uphole (from a high pressure region to a low pressure region). If the kick is allowed to reach the surface, drilling fluid, well tools, and other drilling structures may be blown out of the wellbore. These xe2x80x9cblowoutsxe2x80x9d often result in catastrophic destruction of the drilling equipment (including, for example, the drilling rig) and in substantial injury or death of rig personnel.
Because of the risk of blowouts, blowout preventers are typically installed at the surface or on the sea floor in deep water drilling arrangements so that kicks may be adequately controlled and xe2x80x9ccirculated outxe2x80x9d of the system. Blowout preventers may be activated to effectively seal in a wellbore until active measures can be taken to control the kick. There are several types of blowout preventers, the most common of which are annular blowout preventers and ram-type blowout preventers.
Annular blowout preventers typically comprise annular elastomer xe2x80x9cpackersxe2x80x9d that may be activated (e.g., inflated) to encapsulate drillpipe and well tools and completely seal the wellbore. A second type of the blowout preventer is the ram-type blowout preventer. Ram-type preventers typically comprise a body and at least two oppositely disposed bonnets. The bonnets are generally secured to the body about their circumference with, for example, bolts. Alternatively, bonnets may be secured to the body with a hinge and bolts so that the bonnet may be rotated to the side for maintenance access.
Interior of each bonnet is a piston actuated ram. The rams may be either pipe rams (which, when activated, move to engage and surround drillpipe and well tools to seal the wellbore) or shear rams (which, when activated, move to engage and physically shear any drillpipe or well tools in the wellbore). The rams are typically located opposite of each other and, whether pipe rams or shear rams, the rams typically seal against one another proximate a center of the wellbore in order to completely seal the wellbore.
As with any tool used in drilling oil and gas wells, blowout preventers must be regularly maintained. For example, blowout preventers comprise high pressure seals between the bonnets and the body of the BOP. The high pressure seals in many instances are elastomer seals. The elastomer seals must be regularly checked to ensure that the elastomer has not been cut, permanently deformed, or deteriorated by, for example, chemical reaction with the drilling fluid in the wellbore. Moreover, it is often desirable to replace pipe rams with shear rams, or vice versa, to provide different well control options. Therefore, it is important that the blowout preventer includes bonnets that are easily removable so that interior components, such as the rams, may be accessed and maintained.
Developing blowout preventers that are easy to maintain is a difficult task. For example, as previously mentioned, bonnets are typically connected to the BOP body by bolts or a combination of a hinge and bolts. The bolts must be highly torqued in order to maintain a seal between a bonnet door and the BOP body. The seal between the bonnet and the BOP body is generally a face seal, and the seal must be able to withstand the very high pressures present in the wellbore.
As a result, special tools and equipment are necessary to install and remove the bonnet doors and bonnets so that the interior of the BOP body may be accessed. The time required to install and remove the bolts connecting the bonnet doors to the BOP body results in rig downtime, which is both expensive and inefficient. Moreover, substantially large bolts and a nearly complete xe2x80x9cbolt circlexe2x80x9d around the circumference of the bonnet door are generally required to provide sufficient force to hold the bonnet door against the body of the BOP. The size of the bolts and the bolt circle may increase a xe2x80x9cstack heightxe2x80x9d of the BOP. It is common practice to operate a xe2x80x9cstackxe2x80x9d of BOPs (where several BOPs are installed in a vertical relationship), and a minimized stack height is desirable in drilling operations.
Several attempts have been made to reduce stack height and the time required to access the interior of the BOP. U.S. Pat. No. 5,655,745 issued to Morrill shows a pressure energized seal carrier that eliminates the face seal between the bonnet door and the BOP body. The BOP shown in the ""745 patent enables the use of fewer, smaller bolts in less than a complete bolt circle for securing the bonnet to the body. Moreover, the ""745 patent shows that a hinge may be used in place of at least some of the bolts.
U.S. Pat. No. 5,897,094 issued to Brugman et al. discloses an improved BOP door connection that includes upper and lower connector bars for securing bonnets to the BOP. The improved BOP door connection of the ""094 patent does not use bolts to secure the bonnets to the BOP and discloses a design that seeks to minimize a stack height of the BOP.
In one aspect, the invention comprises a rotatable mount for a blowout preventer bonnet. The rotatable mount comprises a slide mounting bar slidably coupled to a body of the blowout preventer and adapted to move along an axis of a side opening of the body. A swivel is coupled to the mounting bar and to the bonnet so that the swivel enables the bonnet to rotate when the bonnet is disengaged from the body of the blowout preventer.
In another aspect, the invention comprises a rotatable mount for a blowout preventer bonnet comprising at least one rod coupled to a body of the blowout preventer. A slide mounting bar is slidably coupled to the at least one rod and is adapted to move along an axis of a side opening of the body of the blowout preventer. A swivel is coupled to the slide mounting bar, and the swivel is adapted to enable rotation of the bonnet when the bonnet is disengaged from the body of the blowout preventer.
In another aspect, the invention comprises a method for accessing a ram cooperatively attached to a bonnet of a blowout preventer. The method comprises disengaging the bonnet from the blowout preventer and sliding the bonnet axially away from the body in a direction parallel to an axis of a side opening of the body. The bonnet is then rotated with respect to the body about a rotational axis of the bonnet that intersect an axial centerline of the bonnet and the ram is vertically accessed.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.